Precision inertial navigation systems are used in civil and military aviation, missiles and other projectiles, submarines and other underwater vehicles, space exploration technology, as well as in numerous other vehicle applications. A typical inertial navigation system (INS) measures the position and attitude of a vehicle by measuring the accelerations and rotations applied to the vehicle's inertial frame of reference. Since the typical INS is not dependent on other points of reference, it is resistant to jamming and deception.
An INS usually includes an inertial measurement unit (IMU) combined with control mechanisms, allowing the path of a vehicle to be controlled according to the position determined by the INS. An IMU contains instruments for position monitoring. The typical INS requires concentric sets of ball bearing supported gimbals that allow instruments to freely rotate in vehicle maneuvers and further allow for manipulation during a calibration routine.
A typical inertial sensor assembly (ISA) within the IMU is an electronic device that contains internally embedded instrumentation (e.g., one or more accelerometers and gyroscopes) that communicates with other vehicle systems. Data from the internally embedded instrumentation is typically communicated to the other vehicle systems through moving contact devices, such as slip rings or twist caps. The slip rings and twist caps provide a constant communication link for the data without restricting the movement of the ISA.
An INS typically uses either gyrostablized platforms or ‘strapdown’ systems. The gyrostabilized system allows a vehicle's roll, pitch and yaw angles to be measured directly at the bearings of the gimbals. The INS is traditionally rotated using electromagnetic motors on a ball bearing supported gimbal axis. Disadvantages of this scheme is that it employs multiple expensive precision mechanical parts including moving parts that can wear out or jam, and is vulnerable to gimbal lock. In addition, for each degree of freedom, another gimbal is required thus increasing the size and complexity of the INS. Therefore, to get complete three dimensional calibration, at least three gimbals are needed. In strapdown systems, lightweight computers eliminate the need for gimbals, and the sensors are simply strapped to the vehicle. This reduces the cost, eliminates gimbal lock, removes the need for some calibrations, and increases reliability by eliminating some of the moving parts.
Another type of INS floats a sensor assembly with neutral buoyancy in a fluid. This approach requires an extremely complex assembly, sensitive temperature control, and sealing challenges that add considerably to the cost of deployment and maintenance. Also, many of these fluids are hazardous or require a high degree of purity.
Inertial navigation systems that use spherical gas bearings typically require very tight tolerances on the surrounding support shell. These tight tolerances increase the cost of the system and limit the design flexibility of the system.